Remove the unused struct block_op pointer that was inadvertantly
introduced, via cut-and-paste of previous brb_op() code, as part of
commit 
50dd842ad.
(Cc'ing stable@ because commit 
50dd842ad did)
Fixes: 50dd842ad ("dm space map metadata: fix ref counting bug when bootstrapping a new space map")
Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
 
 static int brb_pop(struct bop_ring_buffer *brb)
 {
-       struct block_op *bop;
-
        if (brb_empty(brb))
                return -ENODATA;
 
-       bop = brb->bops + brb->begin;
        brb->begin = brb_next(brb, brb->begin);
 
        return 0;